Diesel cars are sometimes refueled with gasoline by mistake. Already small amounts of gasoline are harmful for diesel fuel's lubricity, cetane number, viscosity and flash point, and may cause vapor bubbles. Cases are laborious to fix. Repair costs may be thousands of euros if fuel injection system break down has taken place.
Misfueling of diesel fuel into gasoline is not common in cars but may take place in non-road engines refueled from canisters. This will cause engine oil dilution, reduced octane number and running problems. Adding of SCR-urea into fuels causes serious problems. Coolant and windshield washing concentrate may be added thinking that they help to dissolve water into fuel; only additives indented for fuels shall be used.
Practice has shown that even automotive professionals may not know which misfuelings are serious and which are harmless. Some misleading advice has also been distributed by the media. Old rules allowing gasoline in diesel fuel in order to enhance cold operability are not valid with modern fuel injection systems.